Light emitting diodes (LEDs) emit light when voltages are applied to p-type and n-type layers sandwiching a light emitting active layer. Traditional methods of fabricating LEDs consist of growing and patterning epitaxial layers of semiconductor materials on a wafer having a growth substrate using semiconductor manufacturing processes. To increase light extraction efficiency from the LEDs, regions of the n-type layer adjacent to the LEDs are etched to obtain a roughened surface. The roughened surface of the n-type layer acts as a scattering mirror to reflect upward light emitted from the active layer and to reduce internal reflection of light trapped within the n-type layer. To obtain the roughened surface, epitaxial layers adjacent to LEDs are etched to expose the n-type layer, a passivation layer is deposited to cover sidewalls of the LEDs to protect the active layer, and the exposed n-type layer is further etched by a wet etching or a plasma etching process to roughen its surface.
While existing methods of fabricating LEDs have generally been adequate for many purposes, they have not been entirely satisfactory. For example, etching the epitaxial layers to expose the n-type layer may damage sidewalls of the active layer, resulting in electrical leakage paths and a reduction in quantum efficiency of the LEDs. In addition, depositing a passivation layer to protect sidewalls of the active layer incurs extra manufacturing time and cost. Furthermore, the passivation layer does not completely protect sidewalls of the active layer from the roughening process, causing further increases in leakage paths and degradation in quantum efficiency. Accordingly, there is a need for LED fabrication methods that increase light extraction and quantum efficiencies of the LEDs without adding manufacturing complexities.
Embodiments of the present disclosure and their advantages are best understood by referring to the detailed description that follows. It should be appreciated that like reference numerals are used to identify like elements illustrated in one or more of the figures.